Diet1. Mind the Fat High-fat diets can make your immune system “less functional and more sluggish,” Simin Nikbin Meydani, the associate director of the Jean Mayer USDA Human Nutrition Research Center on Aging, at Tufts University, in Boston, said.

In fact, a Tufts study compared the effects on immune function of a typical Western diet (containing 38 percent fat) to those of a cholesterol-lowering diet (28 percent fat) and discovered that the lower-fat diet enhanced the functioning of T lymphocytes (or T cells), which help ward off infections.

Aim to get 25 to 30 percent of your total daily calories from fat, with most of those coming from monounsaturated fats (found in olive oil, avocados, and peanut butter) and polyunsaturated fats (think sunflower and corn oils, salmon, and walnuts). Limit saturated fats (such as those in whole milk, butter, and high-fat meats) and trans fats (which are listed on labels as partially hydrogenated oils).

2. Eat Plenty of Protein The amino acids in protein are the building blocks of the cells in your immune system, and they help create protective white blood cells and antibodies.

“These cells then block invading pathogens,” Meydani said.

Women should consume approximately 50 grams of protein a day (about 60 to 75 grams a day during pregnancy) or get at least 10 to 15 percent of their daily calories from protein. Choose lean protein, such as fish, skinless poultry, eggs, beans, low-fat cuts of beef, or soy products.

Exercise3. Stay in Motion According to several studies, moderate exercise (walking briskly, cycling, or swimming for 45 minutes, five times a week) has been shown to enhance your body’s defenses and even cut down sick days by up to 50 percent.

Aerobic exercise enhances blood flow, and “the circulatory system is the route of transport for those cells that fight off infection,” David Katz, an internist and the director of the Yale University Prevention Research Center, in Derby, Connecticut, said. But don’t assume that more exercise makes for superhuman bug resistance. Studies have revealed that prolonged, vigorous exercise (like running a marathon) can compromise immunity after the workout.

4. Fit Into Your Skinny Jeans In a study conducted at Tufts University, researchers put slightly overweight adults with elevated cholesterol levels on a low-fat diet. After 12 weeks, the subjects had lost weight and lowered their cholesterol. More surprising, their T-cell function had noticeably improved.

“And we’re not talking about drastic weight loss,” Meydani said. “Losing even a few pounds can yield an improvement in how well your immune cells function.” To drop a pound a week, each day aim to trim 250 calories from your diet and burn 250 calories through exercise.

Belt It Out5. Show Off Your Musical Talents Research conducted at Johann Wolfgang Goethe University, in Frankfurt, indicates that singing helps improve both a person’s mood and the levels of antibodies that protect from invading germs.

Also, a study at Willamette University, in Salem, Oregon, found that when people played percussion instruments, like the drums, and sang along, they showed greater concentrations of these antibodies than did those who simply listened to music. This is an example of how something that is enjoyable is also good for you, Carl Charnetski,a professor of psychology at Wilkes University, in Wilkes-Barre, Pennsylvania, said.

Love Your Pets6. Pet Something Fluffy Strange but true: A study conducted at Wilkes University found that stroking a dog for 18 minutes led to a significant spike in secretory immunoglobulin A (IgA), which helps protect the body against germs trying to enter it. Again, chalk this up to the power of pleasure, Charnetski said, which triggers the release of chemicals in the brain that enhance immune function. That’s why it pays to pet your dog or cat (or your neighbor’s) as often as possible.

If you’re not an animal lover, don’t worry. A study conducted at the University of Zurich revealed that touching a loved one in an affectionate way―rubbing each other’s shoulders or neck, say―has a similar effect. A simple act like that can help lower levels of the stress hormone cortisol, which can hamper white blood cell function.

Consume Good-for-You Foods7. Get Three Colors in Every Meal Fruits and vegetables in reds, oranges, yellows, and greens, are especially rich in carotenoids, which help immune cells surround and kill off a virus. They also contain antioxidants and vitamins A and C, which strengthen cells and help them defend against invading bacteria, Charles Stephensen, a research scientist with the U.S. Department of Agriculture’s Western Human Nutrition Research Center, at the University of California, Davis, said. Aim for five to nine servings of produce a day, which is easier to do than you may think: Have at least one serving at each meal and two as snacks and―bingo―you’ve already reached five.

8. Eat Good Bacteria "Studies on specific probiotic products have shown that their ‘good bacteria’ can help prevent or reduce the duration of some gastrointestinal, urogenital, and respiratory illnesses,” Gregor Reid, a scientist at the Lawson Health Research Institute, in London, Canada, said.

Probiotic foods or supplements can be found in foods that are easy to incorporate into your daily diet. Look for probiotic yogurts (such as Dannon Activia and DanActive), tempeh, fortified cheeses, and kefir drinks. Be sure to choose probiotic foods or supplements that contain proven strains, such as Lactobacillus rhamnosus GR-1 or GG, L. casei Immunitas, and Bifidobacterium animalis DN 114 001; don’t rely just on the words PROBIOTIC or ACIDOPHILUS on the label.

Rest Up9. Make Late Nights an Exception Set aside ample time to get the restorative shut-eye that your body needs (most experts advise seven to nine hours a night). In a study conducted at the Mount Sinai School of Medicine, in New York City, women who were well rested had more active killer cells (white blood cells that attack germs) than did women who felt tired. To make sure you nod off quickly, keep your room cool, quiet, and dark. Try to avoid caffeine, alcohol, and strenuous exercise at least three hours before bedtime.

10. Resolve to Really Relax Carve out time for whatever helps you unwind―be it yoga, painting, or crossword puzzles―on a regular basis, and ideally every day.

“That chronic, teeth-grinding kind of stress suppresses circulation of your immune cells, inhibits your body’s responses to invaders, and elevates levels of cortisol,” said Bruce McEwen, the director of the Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, at Rockefeller University, in New York City.